1. Field of the Invention
The present invention relates to a waveform generator that generates a lamp wave, a waveform shaper that shapes a lamp wave, and a testing apparatus that tests an AD converter. More particularly, the present invention relates to a waveform generator and a waveform shaper that generate a lamp wave with a low noise.
2. Related Art
Conventionally, as a method for testing an analog-digital converter (hereinafter, referred to as an ADC), a method for inputting a lamp wave into the ADC and testing whether the ADC normally operates in a voltage range of the lamp wave has been known. Here, a lamp wave is a waveform in which a voltage value linearly changes in a predetermined voltage range.
Moreover, it is desired to reduce a test cost in testing a device such as an ADC. As a method for reducing a test cost, it has been known to enhance a test throughput. For example, in testing an ADC by using a lamp wave, it is possible to shorten a testing time per one ADC and enhance a test throughput by using a high-speed lamp wave.
However, when a high-speed lamp wave is used in testing an ADC, it is necessary to broaden a bandwidth of a test circuit because inclination of the lamp wave becomes sharp. When a test circuit has an insufficient bandwidth, a distortion of a lamp waveform occurs. Moreover, when a bandwidth of a test circuit is broadened, noises overlapped on a lamp wave increases and thus a measurement variation increase. In this manner, in a conventional apparatus, it was difficult to generate a high-speed and low-noise lamp wave. For this reason, it was difficult to enhance a test throughput of an ADC.